1. Field of the Invention
This invention relates generally to the field of heating, ventilating, and air conditioning systems. More particularly, the present invention comprises a heat pump with an integrated pressure reducer for reducing compressor workload in the cooling and heating cycles.
2. Description of the Related Art
Various heating, ventilating, and air conditioning (HVAC) systems are known in the prior art. Heat pumps are HVAC systems which use a circulating refrigerant as a medium to absorb and move heat from the space to be cooled to another space and subsequently dump the absorbed heat out of the system. Heat pumps typically employ a reversing valve which allows the refrigerant to be circulated in one direction for cooling applications and another direction for heating applications.
A simplified schematic view of a HVAC heat pump is illustrated in FIGS. 1 and 2. Heat pump 10 includes compressor 12 which is supplied with a liquefied refrigerant from accumulator 14. FIG. 1 shows heat pump operating in a cooling state. In the cooling state, heat is collected from the inside of a house through interior coil 20 (acting as an evaporator) and rejected to the atmosphere through exterior coil 18 (acting as a condenser). Reversing valve 16 directs a stream of hot compressed gas to exterior coil 18 where heat is transferred to an outdoor heat sink. Although not shown in this illustration, a fan is typically used to increase convective heat transfer via exterior coil 18. As heat is rejected to the heat sink (atmosphere) in exterior coil 18, the hot compressed gas turns into a hot condensed liquid. The hot condensed liquid stream passes through bypass valve 24 in the direction of interior coil 20. At the entrance of interior coil 20, the hot condensed liquid passes through thermal expansion valve 26 where the stream expands into a cooled vapor stream. The cooled vapor stream passes through interior coil 20 and collects indoor heat. A receiver or dryer is typically used to collect condensed moisture, but has been omitted in the view. The cooled vapor stream eventually passes through reversing valve 16 and back to accumulator 14.
FIG. 2 illustrates heat pump 10 operating in the heating mode. In the heating mode, reversing valve 16 directs a stream of hot compressed vapor from compressor 12 to interior coil 20 (which is acting as a condenser). Heat is released to the inside of the house when the hot compressed vapor stream passes through interior coil. A fan is customarily used to facilitate heat transfer via interior coil 20. As heat is released through interior coil 20 the compressed vapor stream turns to a liquid state. The liquefied refrigerant stream passes through bypass valve 28 in the direction of exterior coil 18. The liquefied refrigerant stream then passes through thermal expansion valve 22 where the refrigerant becomes a vapor and absorbs heat from the outside passing through exterior coil 18 (which is acting as evaporator). The vapor refrigerant is then directed back through reversing valve 16 to accumulator 14.
The heating mode performance of HVAC systems are typically evaluated in terms of coefficients of performance (COP), and cooling mode performance is evaluated in terms of energy efficiency ratio (EER) or seasonal energy efficiency ratio (SEER). EER is essentially the ratio of cooling capacity in Btu/Hr and the input power in watts (W) at a given operating point. SEER is related to EER. While EER is evaluated with respect to a specific internal and external temperature, the SEER is determined over a range of expected external temperatures (the normal temperature distribution for the geographical location of the SEER test).
The amount of input power required to operate a heat pump is principally dictated by the workload and efficiency of the compressor. In the cooling mode, the compressor must generate a sufficient pressure differential to drive a hot compressed vapor stream through a thermal expansion valve. When cooling demands are elevated, the compressor requires even more input power.
Because energy costs for driving HVAC systems are so substantial, measures which improve a systems energy efficiency ratio and/or reduce the compressors workload are needed.